This invention relates to semiconductor circuits comprising a plurality of successive regions of alternating conductivity types, and in particular, to a low leakage junction isolated four-region semiconductor crosspoint switching structure useful in telephone switching systems.
Arrays of Silicon Controlled Rectifiers (SCRs), which are characterized by a low impedance "conducting" state ("on" state) and a high impedance "blocking" state ("off" state, "nonconducting" state) have been suggested as replacements for mechanical relays in telephone switching systems. A PNPN structure fabricated in a p-type silicon substrate can be operated as an SCR.
U.S. Pat. No. 3,786,425, in which there is a common assignee with the present patent application and one common inventor, illustrates a PNPN semiconductor structure consisting of four alternating conductivity type regions in a semiconductor substrate. One of the problems of this structure is that the leakage into the substrate is too high to tolerate in large telephone switching systems.
British Pat. No. 1,427,261 describes a semiconductor crosspoint switch structure having five alternating conductivity type regions contained within a semiconductor substrate. The structure disclosed solves many of the leakage problems of prior art structures; however, the disclosed structure requires an extra semiconductor region which complicates the fabrication process and increases the physical size of the structure.
It would be desirable to have a semiconductor crosspoint structure which comprises four regions of alternate conductivity type in a semiconductor substrate and has relatively low leakage into the substrate.